This invention relates to electromagnetically operated shutters for cameras, and more particularly to improvements of such shutter.
It is known to provide for a camera with a shutter for the drive source of which relies upon a mechanical power or tensioned spring. That is, the spring charged at the time of film winding up is once locked, and when to actuate a shutter release, this lock is released, causing the shutter to be driven to move.
In such spring-powered shutter, it is natural to provide a lock member of the character described above so that the once charged spring as the drive source is prevented from releasing the power before the shutter release is actuated.
For the shutter device utilizing an electromagnetic force as the drive power, however, it is substantially unnecessary to have what is called the lock member since the shutter blades will not be positively driven to move unless supplied with current. The lack of the lock member, however, leads to give rise to a problem that since the shutter when freed from the electromagnetic drive force is retained in the stationary closed position merely under the action of frictional force between the shutter blades, when acceleration is effected due to the gravity, vibrations, or shock, the shutter blades are caused to split off, thereby the film is accidentally exposed. Particularly with the camera often handled in severe working conditions, there is a high possibility of occurrence of such accident. If so, the problem becomes very serious.
It should be also pointed out that the constant energization of the electromagnetic drive source as a counter measure for such problem will lead to a great disadvantage in actual practice.